Conventionally, inkjet printers to perform printing by inkjet scheme have been widely employed (for example, see Japanese Unexamined Patent Publication No. 2003-200565). As inks for use in the inkjet printers, drying-by-evaporation inks have been generally used, for example, water-based inks (aqueous-formulation inks) such as water-based pigment inks, latex inks, and pigment-in-resin dispersion inks, and solvent inks containing organic solvents as solvents. In such cases, a drying-by-evaporation ink refers to an ink to be fixed on a medium by evaporating a solvent in the ink.
In an inkjet printer using a drying-by-evaporation ink such as a water-based ink, the ink is dried by heating by a heater, for example, to prevent bleeding of the ink and perform drying and fixation of the ink. As a more specific method in this case, for example, a method has been known to heat a medium by a heater (print heater) to prevent ink bleeding, and subsequently dry and fix the ink by a postheater (afterheater) such as various kinds of heaters and infrared lamps. As a method for preventing ink bleeding, for example, a method has been conventionally known to form an image-receiving layer of the ink on a printing target medium (medium to be printed).
The contents of the Japanese Unexamined Patent Publication No. 2003-200565 are incorporated herein by reference in their entirety.
In adopting the method for forming the image-receiving layer on the medium, only the specific medium on which the image-receiving layer is formed in advance is to be printed. In this case, a solvent in the ink may remain in the image-receiving layer and cause a disadvantageous circumstance. For example, in a case of a configuration in which a medium is wound up after printing, ink setoff is more likely to occur unfortunately at the time of winding up the medium. When a medium such as paper is used as a base layer under the image-receiving layer, printing using a significant amount of the ink such as printing a color image (color printing) may disadvantageously make curls and cockling of the medium, for example, more likely to occur. In use of a fabric medium such as a dishcloth, there is a need to prepare a medium such as a fabric coated with a pretreatment agent (such as a sizing material), which functions to prevent ink bleeding and assist color development, as the image-receiving layer. In this case, it is necessary to hire a vendor specializing in the pretreatment, which may unfortunately result in time loss and cost increase.
In heating the medium by the print heater to prevent ink bleeding, it is necessary to increase the heating temperature at a position of the platen opposed to inkjet heads so as to speed up printing, for example. In this case, however, increasing the heating temperature causes nozzle surfaces of the inkjet heads to be likewise heated, which unfortunately makes nozzle clogging more likely to occur.
In this case, it is also considered that a solvent having a low boiling point, for example, is used as the solvent in the ink to facilitate evaporation of the ink so as to eliminate or minimize ink bleeding. In this case, however, evaporation of the ink at nozzles is also quickened to disadvantageously increase frequency of nozzle clogging. Consequently, there have conventionally been cases in which use of the drying-by-evaporation ink involves difficulty in reducing ink bleeding.
Disadvantageous phenomena such as ink bleeding caused in use of the drying-by-evaporation ink are particularly noticeable in such cases as increasing the printing speed, and performing deep color printing and both-side printing. The reason is that an increase in the amount of the ink that lands in a unit area per unit time (ejection amount of the ink) makes the ink fail to dry quickly enough. Moreover, in this case, when a medium of paper or fabric, for example, is used, phenomena such as curls and cockling in particular are more likely to occur.
As a method for heating the medium, as described above, the method of additionally heating the medium by the postheater such as an infrared lamp to dry the medium at high speed has been also known. Normally, however, the infrared lamp is not to be switched on and off at high speed. In this case, therefore, it is necessary to constantly keep the postheater such as the infrared lamp in a heating state. As a result, the inkjet heads and other components are also heated constantly to make nozzle clogging or such phenomena more likely to occur. Furthermore, in this case, a condition set to dry the ink at high temperature causes another disadvantageous circumstance that a medium with low heat-resistance is not to be used. In some cases, the medium and the ink may be scorched or discolored.
In use of the infrared lamp, conversion efficiency into infrared light, which is effective for heating, is decreased to cause light including a significant amount of visible light, for example, which is less effective for heating, is to be emitted. In this case, it becomes difficult to effectively heat the ink alone, and it is more likely to heat the medium and components in its vicinity, for example, at the same time. As a result, much of the energy supplied to the infrared lamp ends up as superfluous heat to be released through the medium, for example, and wasted. Eventually, the utilization factor of the energy for drying is decreased.
In use of inks of a plurality of colors, when the inks are heated by the infrared lamp, a difference may be unfortunately caused in how the inks are heated depending on the ink color. More specifically, for example, suppose that inks of colors, yellow (Y), magenta (M), cyan (C), and black (K), are used, and that inks containing pigments as colorants are used. In such a case, only a carbon black pigment of black (K) absorbs more infrared light than inks of the other colors. In view of this, when a setting is made as to intensity of the infrared light to appropriately dry the inks of other colors such as Y, M, and C, the black ink is to be scorched. Conversely, when a setting is made as to intensity of the infrared light in accordance with the black ink, a difference is to be caused in drying levels depending on the ink color.
As inks for use in inkjet printers, conventionally, ultraviolet curable inks (UV inks) that cure when irradiated with ultraviolet light have been also generally used other than the drying-by-evaporation inks. In using an ultraviolet curable ink, the ink is irradiated with ultraviolet light immediately after droplets of the ink have landed on the medium, for example, so as to stop bleeding of the ink on the medium in an instant. In this case, since there is no need to heat the medium, it is unlikely to cause disadvantageous phenomena such as nozzle clogging. In using the ultraviolet curable ink, however, when ink bleeding is stopped by irradiating the ink with ultraviolet light immediately after landing of the ink, the ink is cured before dots of the ink are sufficiently flattened. As a result, the surface of the ink becomes uneven and more likely to be a matte surface. Moreover, the thickness of the ink may become excessively large in some cases. Consequently, a state in which a thin and flat image is printed is not to be obtained appropriately. Depending on uses of printing, there are also cases in which a desired printing quality is unobtainable. In view of this, uses of printing or such factors make it necessary to use the drying-by-evaporation ink instead of the ultraviolet curable ink.
As a configuration that eliminates disadvantages of the ultraviolet curable ink, such as making the surface matte and increasing the thickness of the ink, so as to ensure printing with high glossiness and less unevenness, a configuration of using a solvent UV ink (SUV ink), which is a solution of an ultraviolet curable ink diluted with a solvent, has been also conventionally known. In this case, however, since it becomes necessary to devolatilize the solvent immediately after droplets of the ink have landed, approximately the same disadvantageous phenomena as in the case of using the drying-by-evaporation ink are to be caused.
Conventionally, therefore, there has been a demand for methods to prevent ink bleeding more appropriately in using the drying-by-evaporation ink. In view of this, it is an object of the present disclosure to provide a printer and a printing method that solve the above-described unfortunate circumstances.
The inventor of the present application conducted intensive study on drying-by-evaporation inks in which to perform printing while appropriately eliminating or minimizing ink bleeding. In the intensive study, the inventor first considered directly heating the inks by irradiating the inks with ultraviolet light. In this case, an ink containing an ultraviolet light absorbent is used, for example, and heat generated by the ultraviolet light absorbent irradiated with ultraviolet light is utilized to devolatilize a solvent in the ink. This configuration ensures that, as compared with a case of heating a medium by a device such as a heater, the ink on the medium is heated more directly and more effectively. This configuration also ensures that the ink is quickly dried after the ink has landed on the medium, so as to implement a state in which color bleeding is unlikely to occur.
In order to prevent ink bleeding more appropriately, however, there are cases in which it is preferable to devolatilize the solvent in the ink in a shorter time. For this purpose, it is desirable to add to the ink a substance that generates heat more efficiently when irradiated with ultraviolet light.
In this regard, the inventor of the present application performed various experiments, for example, to find that use of an ink containing an exothermic polymerizable substance and a polymerization initiator ensures drying of the ink in a shorter time. The exothermic polymerizable substance is a substance that generates heat by its polymerization reaction. The polymerization initiator starts the polymerization reaction of the exothermic polymerizable substance in response to ultraviolet irradiation. The inventor also found that this configuration ensures more appropriate prevention of ink bleeding. The inventor of the present application conducted further study and research to find features required for obtaining such effects, which led to the present disclosure.